Question

Zinc can be coated on iron to produce galvanized iron but the reverse is not possible. It is because

• A. zinc is lighter than iron
• B. zinc has lower melting point than iron
• C. zinc has lower negative electrode potential than iron
• D. zinc has higher negative electrode potential than iron

Answer 1

The Correct Option is D

To understand why zinc can be coated on iron to produce galvanized iron but the reverse is not possible, let's delve into the concept of electrode potential, specifically the standard electrode potential related to zinc and iron.

1. Electrode Potential: The electrode potential of a metal is a measure of its ability to push electrons into the circuit, when it is part of an electrochemical cell.
2. Standard Electrode Potential Values: The standard electrode potential of zinc is -0.76\,\text{V}, whereas for iron, it is -0.44\,\text{V}. The negative sign indicates their tendency to lose electrons and form cations.
3. Comparison of Electrode Potentials: Since zinc has a higher negative electrode potential than iron, it implies that zinc is more electropositive than iron. This means zinc is more reactive and has a greater tendency to lose electrons compared to iron.
4. Galvanization Process: In galvanization, zinc acts as a sacrificial anode and protects the underlying iron from rusting. When both metals are in contact, zinc oxidizes (corrodes) instead of iron due to its higher negative electrode potential. This protective action cannot be achieved if iron is coated on zinc, as iron is less electropositive and cannot provide the same level of protection.
5. Conclusion: Therefore, the reason zinc can be coated on iron but not vice versa is due to zinc's higher negative electrode potential than iron. This forms the basis of the galvanization process where zinc offers cathodic protection to iron.

Thus, the correct answer is: zinc has higher negative electrode potential than iron.